Receiver-indicator for radio navigation system of loran type



Aug. l2, 1952 R. R. FREAS, JR

RECEIVER-INDICATOR FOR RADIO NAVIGATION SYSTEM OF LORAN TYPE Filed' March so, 195o 6 Sheets-Sheet 1 BY im ATTORNEY SQ, N

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Aug. 12, 1952 R. R. FEAS, .1R v

RECEIVER-INDICATOR FOR RADIO NAVIGATION SYSTEM' OF LORAN TYPE 6 Sheets-Sheet 2 V.lfileaMarcn so, 4195o EMP FEE:

Enma-f ATTORNEY Aug. 12, 1952 R R, FREAS, JR 2,607,033

4 RECEIVER-INDICATOR FOR RADIO NAVIGATION SYSTEM OF LORAN TYPE Filed March 30, 1950 6 Sheets-Sheet 3 lll/#0,9555

INVENTOR i ATTORNEY R. R. FREAS, JR

Aug. l2, 1952 RECEIVER-INDICATOR FOR' RADIO NAVIGATION SYSTEM OF LORAN TYPE 6 Sheets-Sheet 4 Filed March 50, 1950 w 'l o wf? o wf L Z M M M :al w V| n. w? wml l- MM. 5A m :----IJ 7M. .W Y rfw F Y/WJ 1 wx f Wx@ v Z .HEE MK H 6% f m m 0 7 MMX 7E i ru a5 rz 5 anwv NM F/Y W www uw w@ M mmm M MM2 I0 T \|||\||..J \|l$ d J .4 w Y w w w Y M+ Y; Z l. Z I. Z X

X X1 X INVENTOR Aug. 12, 1952 R R FREAS, JR 2,607,033

RECEIVER-INDICATOR FOR RADIO NAVIGATION SYSTEM OF LORAN TYPE Filed March 30, 1950 6 Sheets-Sheet 5 l L l l 524i/ ma? fwff 61 1': 'Vd Q y W1K/@Lf aff/5%' l Y r l e a, l N C70/2 rmcf Z d @ggg/4 INVENTOR ATTRNEY Aug. 12, I1952 R. R. FREAs, JR

RECEIVER-INDICATOR FOR RADIO NAVIGATION SYSTEM OF LORAN TYPE Filed March 30, 1950 6 Sheets-Sheet 6 ATTO RN EY atenteci ug. 1.2, 1.9523

' OFFICE TION SYSTEM OF LORAN TYPE VRobert R. Freas, YJr., Jermyn, Pa., assignor to;

Radio Corporation of America,'a corporation of v Delaware Application March 3o, 1950, seriaiNo. 152,941 .s A

, 1 'My invention relates to radio navigation systems of the :type utilizing the time difference in the propagation of radiopulses from'synchronized ground stations (known as loran systems?, andparticularly to' an improved receiver-indlcator for use with either a triad transmitter systemor a transmitter system employing two or more pairs of transmitters.

vNavigation systemsv of the above-mentioned typ'emp-loy both the transmitter triads and the transmitter pairs .at the present time. It is desirable vthat the navigation receiver be designed for easy operation with either transmitter triads or transmitter pairs. One aspect of the present invention is the provisionof an improved receiver designed forV such operation. vAnother aspect of theV invention is `the provision of an improved navigation receiver` that may beeasily operated with a transmitter triad, regardless oi Whether the receiver is ever to beoperated with transmitter pairs.

, In an example oi the invention described hereinater, it will be assumed that the transmitter triadconsists of three radio pulse' ground transmitters geographically spaced. One transmitter is referred to as the master transmitter, and the other two transmitters are referred to asA the slave A'transmitters since their pulse transmission is synchronized with that of the master transmitter. v-

TheV master transmitter transmits two pulses during each loran lperiod (identified as L), the pulsesbeing spaced in time by L/2. These pulses are known as the X and Z pulses. One slave transmitter transmits one pulse each loran period, this pulse being known as theY. pulse. The other slave transmitter also transmits one pulse eachloran period, this pulse being .known as the W pulse; In addition, the X pulse is close- 1y Afollowed by` a pulse for the purpose of ldentifying the X pulse'. v Y

As will be apparent: hereinafter, the present invention is practiced by employing index marker reversing switching; .One reading from the triad:is'taken (using pulses X and W) with the fired, 'marker on the'top trace and the Variable Vmarker on the lowertrace, these traces appear- .ing on the indicator tube screen; the next reading (using pulses Z and Y) is taken with the xed marker on the lower trace and thevarlable marker on the top trace. The index markers maybe pulses that produce notches in the traces as illustrated in this application or they may be rectangular pulses, for example, in which case they are commonly reierredto as pedestals.

' s claims. (ci. 34e-103)' Referring now to the transmitter pair arrangement of ground stations where pairs rather than triads are employed,` there are pairsL of geographically spaced synchronizedetransmitting stations .that emit radio pulses Vhaving a iixed time relation.A Each pair of ground; stations preferably transmits pulses at an assigned indiv idual repetition rate .for the purpose of station selection. It may be noted vthat this is true as to each triad group where triads are used. The pulses are broadcast, as in the case of transmitter triads, so that they may be received Vby means of receiver-indicator equipment located in the aircraftsor ships Whose positions are to be determined. v g

By means 0f the receiving equipment, the operator on the craft determines the time difference between the pulses Y.from the two transmitter ,stations of'one pair, or between the pulsesfrom a master transmitter and a slave transmittenof a triad, as they arrive at the receiver., lSincethe radio pulses travel from the ground transmitters to the receiver at a known propagation rate (i.,e., at the velocity of light) itis-known that the-prosition of the craft is at some point on a line corresponding to the time diierence reading; By obtaining the time difference reading from a second pair `of ground stations, or from themaster transmitter and the second slave transmitter of a triad, a second line corresponding to the s econd time difference reading is obtained, andthe intersect point of ,the two lines is the position of the craft. Special maps having the time difference or loran lines printed thereon for the several pairs of ground stations are vprovided for use with the navigation system.

In order to measurethe time difference in the arrival of successive pulses from two synchronized ground stations, the receiving equipment is arranged to generate pulses at selected repetition rates. The pulses may Abe adjusted tohave a definite time relation to time of arrival of, the ground station pulses and are provided forthe purpose of driving or'synchronizing cathode-ray deflecting circuits. The: deflecting` circuits lp'roduce cathode-raysweep traces on which the received ground station pulses are displayed.- These selected-repetition-rate and adjustablydelayed pulses are obtained from a system-,orf counters and switching to be described in detail hereinafter. Y y

For the .purpose offselecting a particularl pair of groundstations or a particular triad, the operator selects the particular pulse 'repetition rate Vfor the` driving or synchronizing 'pulses 'correa sponding to the repetition period of the pulses transmitted from said pair or triad whereby the deflecting circuits may be synchronized with the received pulses from the selected ground stations. This repetition rate selection is accomplished by adjusting the repetition-rate-determining switches of a' chain of lcounters as 1,6- scribed hereinafter. Thus a particular pair or triad of ground stations is selected at the receiver apparatus by setting the said counter switches to preselected positions. Thispreferably is done v by turning a single station selection `kniob'ojzierating the several counter switches. `"Assiirriing'the station selection switches are ganged.the.station selection knob is turned to V'a'lpos'iti'on Vindicated on the receiver panel for obtaining sweep synchronizing pulses having the saine repetition pey l the selected pair of ground stations. 'Now thereceived pulses from the selected ground stations can bemmade to. appear stationary on the cathode-'ray sweep Vlor trace Vwhereas. those received from'other ground'station's will move along the same trace.v

Thepulses from the two .transmitter stations ofla" selected pair are; commonly referredito as Aan'd'B pulses, respectively, Land the B pulse is identified as the pulse that occurs afteror. follows the mid-point- 'of the other pulseperiod. In atriad the Xf and '.W pulses correspond to said A andB pulses, respectively.

'In operation, the A and B (or X and W) pulses are" displayed,- respectively, rst on two slowsWeepcathode-ray"traces and then on two fastsweep cathode-ray traces, thereby enablingfthe operator toobtain an' alignment of the. A and B (or Xfand W) pulses by adjusting another set ofv switches offsaid chain'offcounters, referred to as delay-determining switches, so that;t he time die'rence'betwe'enthe pulses driving or synchroniing the cathode-raydflecting circuits. equals exactly the time'diiference between A and. B (or XadjW), pu1.se o

`It"vfill be note'd'that'thechain oi'counters has twsets of 'switches connected-'to it, one for detrmiing'the'repetition'rate 'and the other for determining 'the 'ai'rll'irit a 'pulse vis delayed; The action' of each" 'isN 'indpeidnt'of the` action' 'of webmail, V. adjustment f or the display and alignment of `tl'ie' `A andB ACor' XandfW) pulses" is 'accomp lish'edby' "first settingthe A (orf'X) Vpulsel at th'elft end of theuppe'r slew-sweep trace, when the,rebeivingapparatusis swithed 'to an operatingp'sitiorixa ked #1T The"B '(or1W) pulse will then appearbn" the Vlower cathode-ray trace and. a variablel index 'marker may nowbe located u'iider the vBiorfW) p'lsefthisbeing done by adjiisting vtleseveral delay switches 'to delay the vwia'ble indeiimarker" the correct amount.` vThe apparatus'fis the'switched toa #2 fast-sweep peration'positior (so thatthe `A andQB (o'iiXand W) pulses 'apar'ntwo fast-sweeptraces, respct ely.V- Thestarting tirneqf the fast-sweep trace on which' theB l(r W) pulse'fappears alviays"- coincidswitlji `the` start fof said- 'variable inieSc-'marker asfdeterrrir'ied by""the delay switches, while the startingftime''of the fastsweep vtrace 'o n'whichthe A (or X) pulse appears, cnids witnftne starter the slow-sweep trace, Therefore, by a more exact adjustment'o'f the' delay'switclies,V `the adjustable fast-sweep waveis caused" to Astart'atfh'e 'propertime to bring the Anand" B."(or"X and'fW) pulses into alignment. In V'order to v'insurexact alignmentg theA and In the specific example herein described, the counter chain comprises four decade counters that divide by 1'0` followed by a frequency divider that divides by 4. The first stage of the divide by 4 unit is a binary counter (a multivibrator) that is the last stage, strictly speaking, of'the counter chain. The second multivibrator of the divide by 4 unit has no reset pulse applied to it. The decade counters are preferably of` the general type described in application See rial No. 580,446, led March 1, 19,45, in the name of Igor E. Grosdoir, now Patent No. 2,521,788, issued September 12, 1950. 4More specifically, the counter and switching combination utilizes prinf ciples described in Patent No. 2,490,500, issued December 6, 1949, in the name. of CharlesA J. Young but includes improvements over and additions to the combination disclosed by Young. As tothe counter and switching system per se, the feature of combining two sets of switches with the counter chain vso that one set ofswitches determines repetition rate while the otherset ofswitches determines delay, is disclosed. and claimed in the application Serial No. 33,846, filed June 1 8, 1948, in the name of John D. Woodward, now/Patent No. 2,523,244, issued September4 19., 1950. The said Woodward application also discloses and claims a loran receiver-indicator. that 1s the same as described in the present'application insofar as voperation with pairsA of ground stations are concerned.

.An object of'. the invention is to provide. improved receiving equipmentforfaV radio navigation system ofthe type utilizing the propagation of radio pulses either from 'pairs of synchronized ground stations'or from a triad of synchronized ground stations.

A still further object of the invention is topro-i vide an improved method of and means for indicating the time,V difference between radic'pulses transmitted from a tria'dof synchronized ground stations. l

A still further object orY the invention is 4to provide an improvedv methodv of and means for obtaining a direct reading of the time difference between radio pulses 'transmitted vfrom a triad of synchronized groundsfstations.

rTheinvention will be better understood from the following description taken inY connection with. the`v accompanyingfdrawing in which:

y Figure 1 is a block andcircuit diagramof navigation receiving apparatus designed iny accord-,- ance with oneA embodiment of the invention;

Figures 2 fand3, to;be placed side byzside, are block andcircuit diagrams of thefcounter andzthe associatedY repetition ratev 'switching' and. delay switching shown in block in Figure 1,

Figure 4 isa block diagram representing atriad oi ground radiotransmitter stations of th'e navi gation system;

Eig. 5 is a group of graphs which are. referred to 1n explaining the operation of the navigation system shown'inlFigure 1f o `apparatus of Figure 1 andof the received pulses as they appear on the traces When'the X vand W pulses are aligned; Y

Figure Bis a View `of the fast-sweep cathoderay traces on the cathode-ray tube indicator and ofthe received Ypulses X and W as theyfappear on the two fast-sweep traces, respectively, during the nextlstep in obtaining more exact alignment of theXandW pulses;

Figure 9 is a viewshowing the fast-sweep traces of Figure 8 superimposed or collapsed for the nal alignment step and showing theX and W pulses exactly* aligned and superimposed; y I

Figures 10 and 11 are circuit diagrams of the horizontal deecting' slow-sweep and fast-sweep circuits, respectively, employed'in the systemof Figure 1;.andvv Figure 12 is a group of views of the indicator screen showing the slow-sweep cathode-ray traces and the received pulses as they appear on said traces during different steps in the process of obtaining a time interval reading; 5'

dicated by similar reference characters. J

THE COUNTER4 CHAIN AND ASSOCIATED REPETI'TION RATE SWITCHES AND. DELAY SWITCHES Referring to the navigationreceiving apparatus shown in Figures 1, 2 and 3,'-the pulse-producing system comprises a crystal oscillatorv l0 that pro.- duces a sine wave voltage ofstable'frequency Whichin the example illustrated is. l megacycle per. second,v the repetition .period being 1 microsecond. -The frequency of the crystal oscillator output may be increased or decreased slightly by a' manual adjustmentas indicated at the control knob ll for obtaining a right or leftdrift, of a received pulse on a cathode-ray sweep trace.

The crystal oscillator VI0 drives a decade counter1-l2 to produce periodic pulses which recur at the rate of 100 kilocycles per second. The repetition period orftiine interval between successive pulses is, therefore, microseconds.

The frequency of the l0 ps. pulses is divided by ten by means of a second decade counter I3 to produce 100 ils. pulses. The frequency of the 100 as. pulses is divided by l0 by means of a third decade counter i4 to produce 1000 ps. pulses. 1 The frequency of the 1000 ps. pulses iis dividedr by 10 by means of a fourth decade counter i6 to pro- 'duce 10,000 aspulses, and the frequency of these is divided by 4 by means of afrequency divider or counter l'! to' produce 40,000 lis. pulses. As explained hereinafter, the decades and the rst stage of the divider Vl1 comprise' a counterchain. The output of divider l'lis'in the form of a square wave having the repetition period of 40,000 as. This square -wave Lis always symmetrical regardless of the repetition rate'since the reset pulses are not applied tothe second and last stage of the divider ll as will be understood from ,the laterY detailed description. 'Ihesquare output wave ofonedpolarity ispassed; through a cathode follower `tube I8y and from it there lis obtained a vertical separation wave. (at lead 369). The said output wave is also supplied overa lead |9811 to a fixed index markeriswitch. The vsame square output wave, but of oppositepolarity, is

passed through a cathode follower 18a and sup-i plied to said index marker switch. By means of saidswitch the-output waveof either polarity may be supplied to a shaping circuit |05 forobtaining-either a pulse |05A or a pulse |0513 (Fig. 5) that drives or synchronizes the fixed horizontal fast-sweep deflection as explained hereinafter. The selected pulse, i. e. either I05Aor 105B, also appears on a slow sweep trace as a fixed index marker. l

The fixed index marker marking switchingas Well as the variable index marker switchingndicat'ed on Fig. 1 will be described in detail in connection with Fig. 2, The amplitude balance switching, which may be omitted if desired,will alsobe described in connection with Fig. 2.

A variable index markerk pulse, which is obf tained from a gate circuit #2, is adjustable in timing or delay whereby it may be shifted along the sweep trace when a slow sweep is used and whereby it may be utilized to trigger the adjust-1 able fast sweep when the fast sweep isV used.

The amount the variable index marker pulse is delayed is determined by the setting of time delay switches SID, 52D, S3D, SGD, and SED. These switches, as shown in Fig. 3 are multi-pole, multicontact switches that are connected to the several anodesvof the multivibrator tubes in the counters. This will be described in detail hereinafter in connection with Figs. 2 and 3. y

'I'he repetition rate of the pulse from gate #2, 'as wel-l as that ofthe other pulsesr taken'oifthe counter chain,including the pulse taken off a gate circuit #1, may be Varied for the purpose of station selection by means of repetition' rate switches SIR, SER, SBR, SliR, and SER which are similar to the delay switches SID, etc. and which are connected to the anodes of the counter tubes in a similar fashion. Pulses taken off the switches SIR,l etc. are passed through the gate circuit #l and are supplied to a pulse generator 49 which may comprise a Thyratron as explained hereinafter.

The pulse output of gate #l is also applied to each of the counters for resetting them as indicated in Fig. 1 and as will be explained in the more detailed description with reference to Figs.

2 and 3. v Y' A detailed description of Figs. 2 and 3 willbe given later, but first the other parts of the-navigation system will be explained. Assuming operationv with pairs of ground stations; it will be as sumed by way of example that the first pair of ground stations transmit the A pulses with a repetition period of 40,000 ils. and transmit the B pulses with a like repetition period; that the second pair of ground stations transmit A and B pulses having a repetition period of 39,900 as.; that the third pair transmits 39,800 its. pulses; that the fourth pair transmits 39,700 ,11s. pulses, etc. It is apparent that for station selection at the receiving apparatus, the operator must be able to select corresponding repetition periods for the output pulses of the counter system which control the cathode-ray deflection cycle; namely, periods of 40,000 as.; 39,900 ps.; 39,800 vfus.; 39,700 ps.; 39,600 as.; etc. Y'

However, it may Ibe preferred to employ a different group of repetition periods than the group of 440,000 as., 39,900 fis., etc. assumed above. For example, repetition periods of 30,000 as., 29,900 lis., etc. may be employed. Or, as another example, repetition periods of 50,000 as., 49,900 fiswetc.

may be employed.

- @Arr-tour .Rar Taitoieassssrairrou At athispoint, it may .be :well to give a description of the operation of..the:receiving apparatus shown in Eig. A1 with particular reference to the cathode-ray fdeecting'wayes andthe cathoderay tube presentation. 1

AIn.|3.ig...5, the graphs Mx-andN show the wave shapes Yof the :slow-'sweep and fast-sweep vhorizontal deflecting waves, respectively, for obtaining the desired cathode-raytraces. The wave V comprises a pair .of vrecurring pulses, the `second of (referred to '.as the variable index marker.) .-adgustable in time and determines the starting time t of .the wave f-y of the-graph M. The starting .time -it-of .thevariable index marker in relation to the xed index marker may be adjusted-by adjusting the switches SID, SZD, etc. (Figs. 1 and) as will be explained hereinafter, for aligning vthe A Vand B pulses. Three function switching positions identied asV positions #1, .#2 and #3 `are used successively in aligning the A and B pulses..A It will be understood that While-thefpulses :A and B and their corresponding fast-sweep traces appear alternately ori-the cathode-ray tube'screen, they appear to the Aeye to occursimultaneously because ofrpersistence of vision, lag of phosphorescence of the screen or both.

As shown in Fig. 5, the B-pulseis theone that occurs vafter the mid-point of the A pulse period, and 'consequently the-time interval, which elapses between the occurrence of a B pulse and the succeeding 1A pulse will be .less than one-half pulse interval. As will be seen in Fig. 5, the start of one fast sweep (iu-i) coincides with the start of a slow tracel whilethe startj of the other fast sweep (f-g) coincides with the variable index marker.

`As already explained, a momentary change of the recurrence rate rwill change the location of the pulses onthe trace by drifting them along the trace. Specificallyit is-possible for the operator to locate the A pulse at the left side of the upper slow trace, which in turn will cause the Bvpulse to fall on the lower trace, andthe variable indexmarker may be made to coincide withthe B pulse. Therefore, when the function switch is turned to position #2, the A pulse'will occur during theutrace described by the fixed fast-sweep defiecting weveni, while the B pulsewill occur during the trace described by the variableY fast- Avner adjustment willpermit the operatorto align the A and B pulses-so that the-time elapsed between the startof the respective fastsweeps ,In the present system, after the and B pulses havebeenaligned with the receiver switched successively to operating positions #1, #.2 and 3, the desired timediference or time interval; is read oithe delay switches S|D,. SZD, SSD, SAD, and SSD (Figs. land-3) Vwhich indicate, respectively, microseconds inunits, tens, hundreds, thousands and multiples of ten thousand. The time interval thus obtained is the amount that the starting time t ofthe variable index marker has been delayed i'n'timewith respect to' the mid-periodd (Fig. '5) of the deflecting wave cycle in order to align the A and B pulses.

`It may be noted that theA upper fasttrace hA-i (illustrate-d in Fig. 8) isV produced--bythe-rst fast-sweep wave h-i of the deiecting Wave W.

8 The .iowerfiest tracef-g (rif-g. ti is produced tv the second tast-sweep wave of 'the -delecting wave W.

GENERAL -DESCRIPTION oF 'CATHODE RAY TRACE Y PRo'DU'CINe CIRCUITS l :Referring to Eig. 1 .and -to the vgraphs of;Fig. -5,

the outputfo'f the ,pulse generator 49 is supplied over a conductor 6|a, to a slow-sweep deecting circuit I|5 .for producing the sawtooth voltage wave'N. f

V'lhe.output -of the ydivider II is a rectangular voltage 'wave which appears with Vone polarity Vat the output of the cathode-follower tube |-8 as the wave C, and with the opposite polarity at the out-put of the cathodeg-follower-tube A|8a as the waveGI.

To produce the fast-sweep wave hof -defleeting wave M (Fig. 5)-the wave C is supplied by way of lead1l98a,;the index marker switch, and a `conductor |98 to va differentiating circuit |05 te produce a pulse A. The pulse 105A 4is also utilized as the fixed index marker of the wave V. The operation with triads wherein the index marker Aswitch is used in both positions will be described later. v

The circuit for producing the variable index marker of wave V comprises the `counter-chain and associateddelayswitching the said marker being obtained-.from-the adjustably ydelayed pulse U taken from the gate #2. It is the wave U that controls the timing of the adjfustable-fast-sweep portion f--g of wave W.

vThe delayed pulse U is supplied over a conductor I |19 to the mixer |176. The mixed waves U and yHIiiA pass through -a v'clipper |2| and appear as the wav-e vV which drives the fast-sweep deflecting 'circuit Y|22 lto produce the wa've f For ytriad.' operation, `a's will be described later, by means 'of suitable variable index marker switching either the delayed pulse U or a delayed pulse `UI .may beselecte'd as the pulse to supply over lconductor |I-9. In the latter c'ase,the pulse UI controls the timing of the 'variable index marker of awave VI (Fig. 5).

When the systemis `in the #l operating position, the iixed and adjustable index marker pulses of the wave V are applied to the vertical deflectin-g ,plate .388 of the indicator tube |39 through a lead 383-, a -switch 350, a resistor `384, and a-lead 38|.

Description of mixer 106, etc.

Referring to Figs. '1 'and 11, the mixer circuit |06 and the 'Clipping circuit I2I function to clip oir the negative pulses of the wave `Io'SA and to mix the 'remaining clipped positive pulses with the pulses U. Thus, the wave V is lobtained at the output 'of the clipper-mixer combination. The mixer I 06, which may consist of two vacuum tubes having a common anode resistor as shown in Fig. ll, reverses the polarity of the pulses. The 4wavesfin the plate circuit of the mixer |06 are ofl equal amplitude due to operation of the tubes in a condition where grid and plate voltage approach equal amplitude. YThe width of the applied pulses U and |05A is short compared to that of the-plate pulses, the width of. the latter being Ycontrolled by a 'capacitore'resistor cornvbinatio'n in the plate circuit and therefore 'being Vii'i'clependeifitof the width of thincoining wave. This capacitor=resistor combination comprises a capacitor CIand the plate resistor RI.

The wave V is Y.supplied to the fast-sweep deflecting circuit |22 shown in detail in Fig. .l1

9i and described hereinafter. The narrow negative pulses of wave V produce the fast-sweep wave M having the useful deflecting' portions and J-'g. The deflecting wavesM and N are applied from the circuits |22 and ||5 through 'a wave.- selecting switch |23 and through a horizontal deflecting amplifier |24 to the horizontal deflecting plates |38 of the cathode-rayY indicator tube |38. As described in Patent No. 2,445,361 issued July 20, 1948, in the names of Garrard Mountjoy, George D. Hulst, Jr. and Earl Schoenfeld and entitled Radio Navigation System, the horizontal deflecting amplifier |24 may be provided with a switch (not shown) for changing thek bias on the amplifier tubes when the function switch is .changed from the slow-sweep position to the fastsweep position and vice versa, thereby insuring optimum efficiency and undistorted gain from the amplifier tubes.

The switch |23 has three contact points and three corresponding switch positions, referred to as operating or function switch positions, which are identified, reading clockwise, as positions #1,

#2, and #3. Y

There are four other operation Y position switches, described hereinafter, that likewise have these three switch positions and which are ganged with the switch |23.

The fast-sweep circuit Referring more specifically to the circuitf|22 for producing the fastsweep wave M, as shown in Fig. 11, the circuit comprises a vacuum tube 3|3 and a pulse-shaping network that comprises two sections consisting of cathode resistors 33| and 332 shunted by capacitors 333 and 334, respectively, identified as network sections 3|1a, and 3||b. The shaping network further comprises a delay line section 3|`|c comprising series resistors 333 and shunt capacitors 331 connected F across the cathode resistor 33| and terminated in a resistor 338 and in the cathode resistor 332. The fast-sweep wave M is taken o the resistor 338 through an adjustable tap 338, the vsetting of which determines the amplitude of the wave M.

In operation, the capacitors of the network sections 3|1a and 3|1b are charged through the anode resistor 34| and the tube 3|8 to a certain voltage level between successive pulses of the wave VV to bring the tap 339 to the voltage e1. Upon the occurrence of each negative pulse of the wave V, the tube 3|6 is driven to cut-off and the capacitors 333 and 334 discharge through the resistors 33| and 332, respectively. The section 3|1a. comprising capacitor 333 and resistor 33| has a fast time constant whereby the discharge of capacitor 333 produces a voltage of steep slope across resistor 33| The section 3|'la comprising capacitor 334 and resistor 332 has a slower time constant whereby the discharge of capacitor 334 produces a voltage of less slope across resistor 332. These two voltages of different slopes appear at the tap 339 as the sum of the two voltages with the voltage of the steeper slope slightly delayed by the delay network section 3 l '|c.

vThe wave. form of the Wave M following the said slight delay is approximately logarithmic.

It should be understood that the fast-sweep wave M need not be of the wave form described and, in fact, may be linear. f

The above-described fast-sweep deiiecting circuit is vdescribed andv claimed in Patent No. 2,463,969 issued March v8, 1949, in the name of George D. Hulst, Jr. 'and entitled Cathode-Ray Deflection Circuit.

As previously noted, the starting time t of the fast-sweep wave f-g is determined by the adjustment o'f the pulse U (and in turn by the variable index. marker of wave V) whereby the start of the wave f-g may be made to precede thereceived B pulse by the same amount that the start of the wave h-i precedes the received A pulse, this being the condition of alignment of the A and B pulses. ItV should'also be noted that the wave -g is identical with the wave 7L-. i whereby exact alignment of the A and B pulses on the cathode-ray traces is obtained (as shown in Fig. 9) whenV the above-described timing relation exists.

An improved fast-sweep circuit described and claimed fin Patent No. 2,449,169 issued September 14, 1948, in the names of Paul F. J. Holst and Loren R. Kirkwood and entitled Deflecting'Circuits, may be employed if desired.

y The slow-sweep circuit itive bias is applied to the cathode of the tube 3 |8 by connecting the lower end of cathode resistor 342 to the junction point of a pair of bleeder resistorsV 3|9- and 320. This prevents the -tube 3|8 -from drawing currentv at the end of the sawtooth cycle so that ilattening of the sawtooth wave is avoided. The operation is as follows: Eachztimeone of the positive 20,000 as. pulses from the lead 6|a is supplied to the grid of the tube 3|8 by way of a coupling capacitor 32|, the capacitor 343 is charged suddenly from the anode voltage supplythrough the vtube 3|8 to a certain voltage level to bring the tap 344 to the voltage level ez (.Fig.,5) Atthe end of each positive pulse, the capacitor 343 discharges slowly through the resistors 342 and 3|9 thus producing successively the slow-sweep` sawtooth wave portion a-b and the sawtooth wave portion c-d at the tap 344. In Figs. 10 and 11, the values of certain circuit elements vhave been indicated, merely by way of example, in ohms, megohms, microfarads V,and micro-microfarads.

` Tian RADIO The A and -B pulses from a pair of ground stations, or theV XZ, YandW pulses from a triad (Fig. 4), are received bya radio receiver-of the superheterodyne type comprising a radio frequency amplifier indicated at 38|, a converter 362, an I.F. amplifier 383 and a second detector and video frequency amplifier 334. The A and B pulses are supplied with positive polarity over a conductor 383, a conductor 38| and a capacitor 382 to the upper vertical deflecting plate 36B. Thus, the A and B pulses may be made-to appear, as shown inFigs. 7, 8 and 9,'-on`the horizontal cathode-ray traces. The A and B pulses are made `to appear with equal amplitude on ther cathode- I al1-ated; as illustratedfin Eig; '7;' w-liiletlfie-y receiver is: on'. thef 1 operatioxrl position. by-f means of the rectangular wave (E:V (Fig. 5) supplied? from; the cathodeffollower tube: l (Figi. 1) overaconductor 369 to the #1 contact point cfa trace separation switch 31:1, and-1 overa conductor 312.' to. the upper d'eiectingplate"k SESS of? the ca-thoderay' tube |35'. Thus, the? portion' ofi the wave' @,whiclrisJpositireas it appears' on! the' lippen' platef- 3.68; holds thev cathode-ray de'flectic'm;y up acertain amount during-'the occurrence oflthefslowssweep deneetfi'n'gf Waiver cl-d Y e Theiast-swe'ep traces f-e-gfand; h--i are. sep"- arateri' as iliustiatedin Fig; 8-dur1ingithe #2. operationpositional'so `byfmeans ofthe-:rectangular WLVetiC. 'l

rusaswccp- Bmmnisc Blanking is provided so that only the traces f-g andl h-i appear on the. cathode-ray" screen wheninthe #2 and #3' fast-sweep operatingpositions;.Y This blanking is'provided. by means of the negativeportions of'thewave Q. as it' appears on the anode ofthe tube. 31 (Eig. 11')` of` the fast-sweep defl'ecting circuit I'2`Z. The wave Q is supplied fromk the' anode of tube 3|6 to the #2 and #3 contact points of a switch 32| whereby inthel #2 and #3 operation. positions; this Wave i's'supplied over'conductorsSZZ and 326 t'othegrid 321 'of' the' cathode-raytube' l3'9".

- .lEIActiBIttI-JlBI-'ANGE'GGN'DBOL The" diode 3'2 t" isf providedV to control they bril- I'i'ancef of:Y the traces on the cathode-ray tube fsereei'rbyA preventing" changes in bi'asljon4 the cathod'eeray'tube grid-` 3251 dueL to the application ofifblaniking' pulses.V A- leak" resistor' 3-28isfeoI-1'- netted across the diode 31254i andthe cathode of th'e'jdiode 324-' is', connected to a variable bias voltageisource (fno'tl shown). e

Y In' operation, during the periods that the blank'- waves are: positive atlY the' anode' ofthediode the 'impedance of'Y theLA docle- 324 is' very'l'ow sothat' itsianodel is practically a't the bias poten# nali ofits cathode; "Inus, regardless or' the. form of the* blanking'wave and regardless-of Vwhetliier any'blanking wave is being applied, the' voltage on the/grid 321l of theI cathode-ray tubey during' the cathode-rayv sweeps' issubstantiallythe-volitage on the'cathode of'thedi'od'e'" 34f2 DIFFERENTIAL GAIN-#CONTROL CIRCUIT j A diierential gain control circuitv for theRl-F. amplifier 3ft-ly of the radioere'cei-ver preferably vis provided, as shown in Fig. l, foieV the purpose of keeping the amplitudes of the A and B pulses, for example, substantially alike at the receiver outpuathus-L facilitating the'Ai and. B pulse. alignmentfor; in` the:` case of triad operation, the X and' W pulse alignment and the: Z and Y pulse alignment. gain: control` circuit includes a resistor: 343 connected' between the anodes of the'two tubes of the last multivibrator in the 4xIalf-divi'der l'T (Figs.' 1: andfZ-J This connection maybe.r made by way' of a` reversing switch, as explained: hereinafter, tofacilitate operation with triacls. An adjustable: differential gairr balance .tap-on resistor 34% may be moved to either side age'. at. the gaine balances-.topi is supplied through aile'ad:34(l`,.acapacitor 344. and a' resistor 34.6 to the: anode of: a' diodet 341 and to the #-1, #2; and #3 contact points of'a' differenial gainv control switch 3481 Thus; when the receiver. is on any one; of4 the'.` operation positions, the differential gain: control voltage is; appliedthrough the switch 348- and' a conductcnf` 349i to the gain control' grid of anamp-liner tube inirtl'ie` R.F. amplifier 361i.

The' d'iiierentiaik gain*- c'ontrol operation with the receiver' oI-r any onefof the' operation. positionsifsasfollows: Y

When the' gain balance'.Y tapv isv at. the center offthe' resistor 343? no voltage wave" is. applied te the diodeftfl. When the' tap' isj onone side of? this center' or balancer position, aY wave ofone polarity is applied to the diode 347i; whenA the tap is on the' other side of' the balance pointe wave of the opposite polarityvv is' applied-to the diode 3473'. The diode' 341 functions tosupply a nega-tive bias duringthe negativehalf-cycle following' a positive cycleV of' an applied wave. For example, a positive half-cycle: causes diode current to charge capacitor 344, andy during the l fol-lowing negati-ve 4 ha-lfcycle, the capacit-'or' 344 #l operationV position for' pulse alignment; a

normal operating-bias voltage is put' on the'RfF'f. amplie'r'3lil-'- I DETAILED DESCRIPTION 0F CoUNTEmCHAINvANn SWITCHING 0F FIGURES 2 AND 3 A more detailed description will now be given describing' the system of' counters, switches' and gates for obtaining pulses of the desired repetition rate andof the'desired v delay.. The. specific system shown in Figs'. 2" and" 3 provides eight different repetition rates of 40,000 cs.; 39,900 fis.; 39,800 as., etc. for selectingany one of eight pairs of. stations according to the settings of' switches SIR, SZR, etc. As to the pulse delay, this particular' system delays a. pulse from Gps. tov over 19,000 us. according to the settings of switches SID, .S2117 etc.,

Referring to Figs. 2 and 3, the chain of counters, the repetition rate switching, the delay switching,l andthe. gating, or coincidence circuits are shown in detailby way of example. Decade counter #1. consistsA of. multi-vibrator-like locking stagesv comprising double triodes- Vil, V2, V3 and V4. These stages each. have two positions of rest at one or. the other of. which they stay locked,

Vwhen tripped thereto, until. some. applied voltage or 4current trips them. againv to locls them in the other position. InV the embodimentshowm ap'- plication. of negativevoltage to. the' anodes. and thenceto the grids of the `locking circuit tubes will reduce current in that tube drawing current and start the tripping action whichY switches the currentvthrough the other-tube. Decade-counters #2, #3. and #4 are similar and tosimplify the diagram have been illustrated by rectangles. The frequency divider or counter #5 is illustrated in detail and comprisesv only two multivibrators Ml andv M2y since i-tdivides by 4. rl'he multivibrators this. counter are similar tov those employed in the decade counters. However, the rst stage (Fig) as will be explained later.

. 13 MI the nal stage of the counter chain. 'The second stage M2 hasno reset pulse applied to it and it does not supply any pulse to the coincidence tube of the repetition rate-system as will be apparent from the following description."

The repetition rate switching Associated with each decade counter is a threepole, ten-position switch (Fig. 3) for determining the pulse repetition rate. These switches 'are referred to as SIR, SZR, SSR, and StR. While ten switch positions are shown for clearnessof explanation, not all of them are useful in selecting the eight stations in the example described. There isalso a single-pole two-point switch SSR for the binary counter M I.

. The switches SIR, SZR, SSR, S4R, and SSR and the Y contacts thereof are coupled to the anodes ofthe locking circuit tubes whereat the potentials frise and fall depending on which tube of Vthe pair isdrawing current.l For example, the anode VIA of the left-hand or A section of the tube VI is connected to alternate contacts of pole PI of the three-pole switch SIR. The anode VIB of the right-hand `or Bsection vof tube VI is connected to the remaining contacts of this pole. VThe anodes V2A, VZB, and VSB of tubes V2 and VS are connected to staggered pairs of contacts of the second pole P2, etc. The basic details of each Vdecade and how it operates .is j

covered fully in Grosdo application Serial No. 580,446, now Patent VNo. 2,521,788, referred to above and consequently, no detailed explanation will be given here. Associated with the binary MI of counter #5 Vis the single-poletwo-position switch S5R that functions with switchesSIR, SZR, etc. for determining the repetition rate. Although not so illustrated, the live switches StR, ,S2R, etc. preferably are ganged so as tobe operated by a single station selection knob.

The basic purpose of the counter circuit is to produce output pulses after theV counters have counteda predetermined number of master oscillator cycles or pulses. The startof the counting, is controlled by a gate ccircuit #l (Fig. l) and. comprising tubes 26, 21,28, 29, S0, and S4 rlhe development of the counter chain output pulses that are to be produced after the predetermined count has been reached is obtained byfcombining the f proper voltages from the anodes of certain tubes in all five counters. For example', to" se1ectl station LI the repetition period of the last multivibrator M2 of counter #5 is made 39,900 microseconds. Since the first stage MI of counter #5 is the nal one in the counter chain to be reset, as explained hereinafter, the desired result is obtained by making the repetition period of its output wave D (Fig. 5) one-half the said period of 39,900 as. or 19,950 its. Therefore the switch SIR on counter #l is set at position 0 which is the units count, the switch SZR on counter #2 is set on position 5 which is the tens count, switch SSR on counter #3 is set on position 9 which is the hundreds count, switch SflR on counter #4 is set on position 9'whichis the thousandscount, and switch -S-ER on counter ,#5 vis set 'on position 1 which is the ten thousands count.

The voltage pulses collected by the switches are Vcombined by means of ve vacuum triodes 26, 21,

28, 29, and 30. The tubes are in conventional circuits including grid leak resistances BR connecting the switches to ground. Each triode is biased by means of a voltage drop across a by- 14 passed cathode resistor. This combination of pulses is obtained by the connections of said switches to the control grids of these ve tubes. The anodes of the tubes are connected together to produce a single pulse, which represents the sum of the collected pulses, and feeds the same by way of resistors S6,` 31, 36, 39 and 4I and common resistor 52a to the grid 33 of a final combining or coincidence tube S4. The tube S4 is connected in an amplifier stage with its grid grounded by a resistor 45 and its cathode grounded by a resistor 46 and its anode connected to the plus terminal of a direct current source. The anode lof amplier tube 34 is coupled bya capacitor il to the control grid 48 of an output tube 49, the purpose of which is to deliver the combined or output pulse to all of the tubes in all of the decade counters and to the tubes in the binary counter MI to trip the same back to their starting position for successive operation of the counter chain and also to deliver a lpulse of the desired repetition rate to the slow sweep generator |by way of the lead 6Ia. A negative bias voltage is applied to the grid 48 of tube 49 through a resistor 45a.

Referring to decade counter #l which has its switch SIR set at position 0, it is noted that for each position of the switch, a different combination of voltages from the eight tubes of the counter are used as explained in the Grosdoif application Serial No. 580,446, now Patent No. 2,521,788. The voltageon the switch SIR as applied to the grid of tube 26 reaches a certain maximum positive value only when the count is at thervalue for which the switch position isset and the final desired output pulse applied to the grid of tube 3B is obtained only when the proper combination of voltages occurs simultaneously on the selected tubes of all five counters. For example, in decade counter #l on the count of 0, the voltages selected by switch SIR are those at the anodes of tubes VIA and V2A and V4A. This combination of three voltages raises the control grid of tube 26 above its cut-o point so that conduction is initiated in tube 26 and the potential on its anode and at resistor 36 falls. The Aprocedure for selecting voltages by the switches lwill bev understood by referring to the graphs of Fig. 6.

The several graphs of Fig. 6 show the voltages appearing at the several anodes of the tubes VI, V2, etc. The graph identified as VIA shows the voltage on the anode of the left-hand or A section of tube VIA, ,for example. The dissymmetrical characteristic of the graphs for the tubes V2 and V3 results from the feed back employed to obtain a decade count as explained in Grosidof application Serial No. 580,446, now Patent No. 2,521,788. The dots indicate the plates that are selected to `obtain a given count. For example, the anodes VIA, V2A, and VA are connected to switch points 0 to obtain the count O when the switch is set on said points 0. A Vsimilar action takes place in tubes 21, 28, 29 and 30 when the proper voltages are obtained by the settings on switches SZR, SSR, S4R, and S5R. When the final pulse which represents the nal combination of voltages from the tubes 26, 21, 28, 29, and 30 is reached, thevoltage applied to the control grid of tube 34 is reduced (negative) to such a point that conduction inthe tube S4 is cut-olf. This action occurs suddenly at the instant the counters of thecounter chain reach the number or count tubes 26,V 21, 28, and'29 may be made conductive is several-rtimes` during the process ofthe-count, Yet the combined voltage applied to the. grid of tube 34: is never sufiicientlynegative to cut this; tube off: until thelv time occurs. When tubes 26 21, 28, 219.' and 30 are simultaneouslyconductive, this- Vvpoint being; when thev counter chain has-.reached thefpredeterminedl count for which it is adjusted; Atthe.- instant when the counter chain produces its output'pulse atA theplateof tube 34, this outrespond-'tothe tubes. 26, 21, 28,` 29` and 30,v and; their associated circuits previously described.

The'coincidence tube 6| (to which the outputs of tubes;56 to 60 are applied) and the Thyratron tube 62 correspond to the tubes 34 and 49, respectively, of the repetition rate switching circuit. The delayed pulses appear on the leadV IIB.

The setting of the switch SID determines the microsecond delay in units, that of switch SZD put, pulse.y is applied to. the pulsengenerator tube determines thedelay in tens, and the. settings of '49. which'v preferably is a Vapor tube Such as a switches saD, saD, and ssndetermine the delay Thyratron so thata large: current. output isvobe in hundreds, thousands, and tens of thousands; tainedk all th@ 01115D1117 terminal 5l 0f the 10211 respectively; For example, if the delay switches resistor 46a. Preferably, thev tube 49 discharges SID, S2D, SSD, S41), and SSD are on positions a'. Capacitor" 49a`WhCh reevesancharge from the l5 85, '1, 6, and 0, respectively, as illustrated, when B-I SOIIICQ thrugh 2 reSSIOIL 49h- Thus a high pulse yalignment on the cathode-ray tube screen energy outputA Pulse iS produced FIOIIl terminal is obtained, then the reading is 6758 microseconds. 5;( the.l pulse isf applied by way of condenser 52. This reading locates one of the navigation or lorandi lead 42. to reset the countersof the counter an Alines of position on the map prepared for ChainV back tothe ZGIO 0r Starting- IJO-sition. This 20 use with the equipment. For convenience inset'- resetting function. isl accomplished by appl-icating the delay switches SID, etc. their ganged tion of the output pulse, which is :positive in switch arms preferably are operated by rotatable polarity. to the grid Circuits of al1 the tubes in knobs ID, 2D, etc. which carry pointers that inthe counters which draw current in the starting dicate the delay setting. DOStOIl- AS previously stated, the reset pulse is It will be noted that since the last counter not applied to the multivibrator M2 of; the frestage supplying pulses to the gate tube 60 is the quency divider Ii'I. binary MI, the coincidence tube 6I would supply Thereason for not applying a reset pulse to the output pulses of a repetition period of 20,0001Ls. multivibrator M2 is that it must supply a. syinor lessa, depending on the selected repetition meti-ical sduarewave (wave C in- Fig. 5) justas 30 period, in the absence of some further circuit inthecase of the Eccles-Jordan oscillator shown action. Double this repetition period is desired, in Minneman application Serial No. 744,239, now of course, for driving the fast-sweep circuit to Patent. No. 21,515,464 issued July 18, 1950. Furobtain the adjustable fast trace ,f-g (Fi-g; 5). thermore, there is no. necessity for applyinga The desired repetition period is obtained by. in reset pulse tothis, last multivibrator for changing eiect, blanking out alternate pulses as indicated the repetition period. This will be understood in Fig. 5 so that only the 40,000 ,11s. repetition pefrom, the following. riod pulse U appears on the lead IIS.

If the desiredl repetition period of the wavev C This blanking effect is obtained by applying to (Fig. 5) from the last multivibrator M2 is to be the grid of gate tube 60 by way of a lead 10 a 39,900 us., it is only necessary to make the repetisquare wave from the last multivibrator M2. Action period of the wave D* (Fig. 5.) from the precording to one feature of the present invention, ceding multivibrator MI 19,950 as. since. the last this square wave is either the wave CI or the wave multivibrator divides by 2. This, of course, is C (Fig. 5) depending upon the position of the accomplished by the resetting action described. variable index marker switch. Both switch posi'- Sirnilarly, for any other repetition period, the tions are used in triad operation as explained in switch SIR, SZR, etc. are set to give they desired detail hereinafter. For operation with pairs of repetition period for the output wave. D of the ground stations (with A and B pulses), the wave flrstmultivibrator MI of counter #5,which repe.- CI is applied to tube 60. With wave CI on the tition period is one-half that of the output wave tube 60, for example, its grid is held negative C. For the particular example assumed, the. difduring the master period (see Fig. 5) whereby ferent switch, settings for selecting eight diierent the pulse from the binary MI cannot pass through pairs. of stations L0, LI., L2 etc. may be charted as tube 60 during said period. follows The amount a pulse is delayed is not affected REPETITION RATE SWITCBING station L0 L1 112 La L4- rs Le L1 Repetition A20,000 419,950v 19,900 19,850 `19,800 119,750 19,700 19,650

o 5 0. s: 1 0r 5 o 5- o 9 Y 9 1 s s 1 7 e 0 9 9 9 I 9Y 9. 9 9 2 1- 1v 1.` 1 1 1 1 The delay switching l by changes in the pulse repetition rate. because The delay switches SID, 52D, S31), S4D- and l'fhe maximum delay desired is less than the short- S5D are similar to the switches illustrated for est-repet1t-1on-perlod of th? Wave D' The re determining the repetition period and they are setting actlon 1s the only thing that would aiect connected to the chain of counters in the same the delay and this does not 00CHF untl the Count- Way` The voltages taken off the delay switches ers have operated for more than the desired pearesupplied to vacuum tubes 56, 5.1, 5859, and 110d 0f delay WthOut any 105s of count duev to 60 which comprise the gate circuit #2 (Fig. l). resetting.

These tubes and their associatedV circuits cor- The delay swtchsettings obviously d0 not aiect therepetition'rate since they do not affect the resetting circuit. 1 l I PROCEDURE 1N MAKING` .A TIME MEASUREMENT WITH PAIBs The suecessive steps in making a measurement ofthe `time 4 interval between theA and vB pulses from ajpairofground stationswill {now be de- Scribe'cllA T Alignment of A and B Vlm Lses PosrrroN #1 After a particular pair of Vground stations has been selected with. .the receiverl set 4on the #1 operationpositiomthe A and B pulses will appear stationary 'on the :two traces and wel. A suitable drift switch such as knob I lof oscillator I'llis operated to driftone 'ofthe' pulses onto the uppertrace c-'d and over the fixed index marker at the left endof this trace. The other pulse will now appear on the lowerl trace a-b. The pulse on the trace' c-d is the A pulse and the/pulse on the tracea-b is-the B pulse. That this is true will be evident byrefe'rring'to the graphs of'":Fig.-.V5.V I l' fNext,v the startingtime.E tfof the variable index marker' of wave V isy adjusted by setting the delay switches SID, S2D, etc. to bring the variable index markerunder the B pulseqThe variable index marker is now carefully adjusted so that its position with respect to the B pulse isr substantially the same as the position of the xed index marker with respect .to the A pulse..

` eosrrroN #a v 1 Next, referring to Fig. 8, the receiver is switched to.the'fastsweep operation position tI-'2l which results in the A and B pulses appearing on the .traces Zzf-i and f g, respectively., As shown in Fg.- ,rthe,start of the variable index marker pulse of wave V determinesthe start-Of the second fast-sweep portion'f-,g-of waveW, the two starting practically simultaneously. By operate ing suitable drift switches such vas .the knob Il of the crystal oscillator l0, the A andB pulses arec lriftecll to the left ends of the traces where they are on themore expanded portion ofgthe fast sweeps- They-are thenfclosely aligned as shown in Fig. 8 by operating one or moren of the delay switches SID, S2D, etc. y

.PosiTIoN #3f Y 'Ifhe final alignmentfof the-A and 13 pulses is done on operation position #3with the two traces f-'y'and h-zf superimposed as shown in Fig. 9. The front edges of the A and B pulses are now exactly aligned, usually by operating only the switch SID. The time reading can now be made from the settings of the delay switches as shown Iby the positions of the pointers on the switch operating knobs ID, 2D, 3D, 4D, and 5D.

For example, if the vpointers of the switch knobs iD, 2D, 3D, 4D,'and 5D read 8, 5, 7, 6and 0, re-

spectively,'the reading is 6758.microseconds.

' -TRIAD OPERA'rIoN First it should be noted that vthe receiverindicator described in this application is the same as idescribed `in Woodward application Serial No. -33,814.6, now Patent No. 2,523,244, except for the switching applied to the multivibrator M2 to- 'gether' .with associated circuits and except for the minor "change that/differential gain control is "employedin all three operations. This latter .chage-islnot a necessary one.

Thev important feature of theprescnt invention is the use of the fixed indexrmarker switching shown in detail in Fig.l 2.j v'The two switches are ganged'as 'indicated by the broken lines. The amplitude balance switching is not essential but may be desirable for some conditions of operation; it is ganged with the marker switches as indicated.

The triad ground stations may operate on the same carrier frequency as the ground station pairs, or all triad stations may operate on a lower carrier frequency, for example. The same pulse repetition rates may be employed for both `triads and pairs, that is, some or all of the available repetition rates may be assigned to triads -instead of to pairs.

The effect of the index'marker switching will now be discussed with reference to certain of lthe graphs in Fig.Y 5.

Eect of fired index marker switching With the xed index marker'switch in the lower position as shown, the front edge of the positive half cycle of wave C produces the pulse IA which becomes the iixed index marker in the wave V. uThis marker appears on the top slow trace c-d (Fig. '7). Also see `wave N. Meanwhile the variable index marker will appear on the bottom slow trace as pointed out below, since the variable index marker switch is on its lower position.

This condition of operation is the same .as described in the above-identied Woodward application, and is the one used to measure the time difference between A and B pulses or, in this case of triad operation, the time difference between the X and W pulses.

Next, tormeasure the time dierence between pulses Z and Y the two index marker switches are moved to their upper positions. Now the wave Cl is applied to lead'lll. The`front edge of the Ypositive half cycle of wave Cl occurs at the midpoint d', i.v e., midway in the loran cycle L. This front edge produces the xedmarker pulse'lllB which now appears at the start of the bottom slowtrace. Thus the position of the iixed marker pulse has been reversed. Meanwhile, as explained below, the position of the variable marker pulse has been reversed also so that it is now on the upper slow trace.

Eject o-f variable indem marker switching With the Variable index marking switch in the lower position as shown, the wave CI is applied over lead l0 to blank the tube 60 (Fig. 3) during the negative half cycle of wave Cl. Thus the first pulse of wave U (shown dotted) is blanked out and the solid line pulse U is the one that produces thevariable index marker of wave V. Thus the variable index marker appears on the bottom slow trace as previously stated. s

Next, with the variable index marker switch in the upper positionlfor alignment of the Z and Y pulses, the wave()` isapplied over lead` 'i0 to the tube 60; The"nega'tive half cycle oi the waveC occurs during the'sec'ond half offthegloran cycle L .and blanksoutthe pulse of wave U occurring` during'that time. This is shown by the wave Ui. It will be seen that nowthat the variable delay pulse, no'w identified as`UI, appears during the first. half of the lorany cycle L. The pulse Ul produces the variable index markershown in wave Vl; which marker appears on the top slow trace. Meanwhile, .the switching has putthe xed vindex markerlEBYon thel'owe'r'slow trace.`

Eieet 'of marker switchingionjast sweeps Ithas ybeen explained that thewavey -V produces the wave'M fortle conditionofaligning fr andB or X and W pulses. `More Specifically, referring to Fig. 5, the fixed index mar-ker of wave 'V 4pro'- duces the fast sweep t-i Vof wave vM;v and the variable index marker o'f wave V produces the variable fast sweep f-t of wave M This is with the index marker switches in their lower position.

With the index marker Vswitches in their upper positionfor the condition of aligning theZ and Y pulses, the wave VI produces the wave M I. More specically, the fixed .index marker .of wave V! produces the-xed sweep of wave Ml which starts at the midpoint D; the variable index marker of wave V-I produces .the variable fast sweep of wave MI. Y

`It will be evident that when the marker pulses are reversed by the marker switching, the fixed and variable fast sweeps are also reversed. Thus, in the first-or lower switch position, the xed fast sweep (wave M) -coincides time with pulse X and the variable 'fast sweep (wave M) coincides Vin time with pulse In`Fig. '5t11econd-ition is shown where pulses Xand W are. aligned. Y

In the second or upper switch-position, the fixed fastsweep (wave'Ml coincides in time with pulse Z; the Variablerfast sweep (waveMl) falls in the same'loran half vperiod as .pulse Y and obviously may be adjusted to coincide in time with the pulse Y. Y Y Y Dierefritza'l gain reversingswitching As shown in detail in Fig. .2, 4differential gain control switching may be provided lif desired. It will be understood that before the pulsesX'andW .are aligned, Vthe tap on resistor 3:43 is adjusted to make said. pulsesof like amplitude on the indicatortuhe screen. Thefpurpose of the switch is to minimize any further adjustment of this tap that may be required before the. pulses Z and Y are aligned. It will beevident that for most positions of the craft carrying. the trec 'eiver-indeaton some further gain balancing adjustment will be required for the Z, Y alignment'even though the gain controlV reversing' switch is employed.

PROCEDURE 1N MAKING A TIME Mmsiorminnrfwirri TRIADS The operation with triads will now vbe summari-Zed with reference tothegraphs of Fig. 1.2.

The lXW y'rrieci-smement First the time interval between the vX vand W pulses is measured. This is done with the index marker switches in their lower position as shown in Fig. 2. The X pulse, which is readily identified since it is closely followed by a second pulse, is drifted to the left end o'f'the top trace andover the fixed index marker as shown in 12a.'

The diierential gain is ladjusted to. make the X and vW pulses of equal amplitude. Next, as shown in Fig. 12b, the variable indexY marker is moved under pulse lW for the slow sweep ali-gn,- ment of pulses X and W. The approximate, XW delay can now be readif desired.

However, an exact XW delay reading is 'obtained by switching: to the #2 function switch position, i. e., tothe first fast sweep position. The X and W pulses now appear as shown in Fig. 8 and are more vexactly aligned. Next Vthe operator switches to the #3"function'switch position to superimpose V`thepu1ses as 'shown in Fig. 9,

anV exact 'alignment isimadat and The ZY measurement To measure the time interval between the Z and Y-pulses', thefindex marker switches (Fig. 2) are Vmoved to their upper'- p'sitionsj -This `reverses the Aindex-markers as shown in 12o. The fixed index marker is now under the Z pulse. The variable index marker isgnow on the upper trace so that it may be shifted under the Y pulse.

The differential gain control tap is adjusted, if necessary, to make the. Zfand Y pulses of 'equal amplitude "as Yshown in Fig'. 1211.. Next vthewaria ble'index marker is .fmovedvunder' the Y 'pulse to align the Z and Y :pulses :'asshown in 12e. An exact ZY delayreading is obtained by next switching successively tothe ftwo fast sweep posi'- tions (zfuifijction switch positions '#2 and #3) and obtaining Aexact pulse alignment :as described in connection with the' XW ydelay`rneasurement.

It `will'b'ev apparent to `thos'e familiar with the opera-tion of loran equipment that' the present invention considerably simplifies the operationfof taking the two time readings where triads are being v`used. In 'this connection .an vimportant point isthat it is n'of longer necessary to `drift the Z pulse tothe leftv end'of the upper 'trace (the Y pulse then falling Y"on the lower trace) morder .to obtain an alignment -oftheZfand Ypulses.

WhatI claim is: i

1. In a radio system wlfier'e-n periodically .recurring X pulses and Wpulses are 'received from a master ground station and a slave ground station, respectively, said vX pulses having the same repetition. period fa's.'said pulses, a cathode rayy tube Aindicator having-'a :screenen which said pulses are "to vappear l'a'nd in which ancathode4 4ray is directed" toward said-screen,` means for producing a square wave having the v'same 'repetition period as Asaid XI and W pulses, the half cycle of `said square lwave"that-'occurs4 during the voccurrence of an X pulse being identified vas the master period, the other half'cycle of'saidsquare wave being 'identified Aas 'the -slave period, Ymeans for pro'di'1c`-i-ng a fixed index marker that occurs during and vinl-'fixedtimewitlrsaid master period. means for "producingga variable indexmarker pulset'hat occurs duringl said slave period and which may be varied to'coincide in time with said W pulse, means for producing two slow sweep defiecting waves that occur during said square wave half'cyclesrespectively means fordeecting said cathode rayrbysaidlsiow vsweep 'waves whereby two tracesV areprcduced on said screen. 'means for-'separating said traces 'to produce an upper vand a lowerftra'ce, means (for making saidxed marker pulse appearon one 'of'saidtraces "and forjmakingjs'aid 'variable j marker v.pulse vappear on the other iof-*sai'dg'tracesfand means for reversing; Vat the willof the operator, said index marker "pulses with respect to 'said-master vand 'slave periodsfwhereby said -'xed index marker pulse occurs lduring Vsaid slave period; -and said variable index markerpulse occurs during said master period. v

2. AnA indicator system Yfor-'opei'a-ti'on 'with a radio Y ground" system Yt'halt includes radio V'tra-nsf- -mi-tter triads andwherei-n periodically recumng X pulses* and W 'pulses are 'recivedl'fromfa master station and a Vfirs-tY slave station, respectively, o'f a triad; said Xrpulsesv having the: same 'repetition VperiodV as said Wipulsesjs'aid indicator system flecting waves, one'of xedrtiming and'the'other pulsev havingl a xed phase with respect to said master period, means for producing a variable index marker pulse that may be adjusted in time within said slave period, means for .producing said adjustable deflectin'g -wave in `response to the occurrence of said. variable index marker pulse whereby the starting time of the adjustable deecting wave may be shifted to alignv the X pulse appearing on the iixed trace with theNV pulse appearing on the adjustablev trace so that the time interval between the X pulse andthe Wpulse may be determined, and meansior reversing the positions ofrsaid index markers with respect to said master and slave periods so that said fixed index marker pulse occurs within said slave period and said variable index marker pulse occurs within said master period whereby` the time interval reading of pulses transmitted from the master station and a second slave station of said triad is facilitated.'

3. A receiver for use in a radio navigation system wherein periodically recurring and evenly time spaced X and Z pulses are received from a master ground station,l wherein W pulses. are received from a first slave ground station and wherein Y pulses are received from a Vsecond slave ground station, said X and Z pulses occurring during periods of equal duration that are identified as master and slave periods, .respectively, said W andY pulses occurring during said slave and master periods, respectively, said receiver comprising means for producing a square wave having the same repetition period as said X pulses, the half cycle of said 'square wave that occurs during the occurrence of an X pulse being identified as said master period, the other half cycle of said square Wave being identined as said slave period, means for producing a fixed index marker that occurs during and in iixed time with said master period, means for producing a variable index marker pulse that occurs during said slave period and which may be varied to coincide in time with said W pulse, means for producing two slow sweep deflecting Waves, a cathode ray tube indicator having a screen on which said pulses are to appear and in which a cathode ray is directed toward said screen, means for defiecting said cathode ray by said slow sweep waves whereby two traces are produced on said screen, means for separating said traces to produce an upper and a lower trace, means for making said xed marker pulse appear on one of said traces and for making said variable marker pulse appear on the other of said traces, and means for reversing the position of said xed marker pulse with respect to said master and slave periods whereby said fixed index marker pulse occurs during said slave period and means for simultaneously reversing the position of said variable index marker pulse with respect to said master and slave periods whereby said variable index marker pulse occurs during said master period.

4. In a radio navigation receiver for measuring'the time interval between received pulses, a cathode ray tube indicator :having a screen and means for producing a cathode ray and directing it lagainst said vscreen,m`eans for producing a square Awave having the.: saine repetition period as that of the pulses to be received, the rst half cycle of v,said square Wave being identified as the master period, the other half lcycle :of said square wavebeing identified as the slave period, means forproducinga iixed index marker that occurs during and in xed time with said master period,v means for producing avariable index marker pulse, that occursduring said slave period and-.which ,may-be Avaried to coincide in time with one ofthe received pulses, means for producing two slow fsweep defiecting waves and means for deiiecting said cathode ray by said slow sweep, waves vwhereby two traces are produced on :said screen, means for separating said traces tovproduce an uppervand a .lower trace, means for making said fixed marker pulse appear cnone of said traces and for making said variable marker pulse appear on the other of said traces, and means Vfor reversing said fixed and variable index marker pulses with respect to said master and lslave periods whereby said fixed index marker pulse occurs during said slave period andsaid `variable index marker pulse occurs during said master period.

Y 5. In a radio navigation receiver for measureing the time interval between received pulses, a cathode raytube indicator having a screen and having means for. producing a cathode ray and directing it againstA said screen, and wherein two similar deiiecting waves, one of fixed timing and the other of adjustable timing, are to be produced for deflecting the cathode ray of said cathode ray tube indicator, means for producing a square wave having the saine repetition period as the received pulses,` the rst half cycle of said square wave being identied Vas the master period, the other halficycle of. said 'square wave being identiiiedas the-slaveA period, means for producing a iixed index marker pulse havinga xed phase with respect to said master period, means for producing a variable index marker pluse that may be adjusted in time within said slave period, means for producing said adjustable deflecting wave in response to the occurrence of said variable indexy marker pulsewhereby the starting time of said adjustable dei'lecting wave may be shifted for the purpose of obtaining pulse alignment,andmeans for VVreversing the positions of said index markers with respect to said master and slave periods so that said-xed index marker pulse occurs Within said slave period and said variable index marker pulse occurs within said master period.

6. In a radio navigation receiver for measuring the time interval between received pulses, a cathode ray tube indicator having a screen and means for producing a cathode ray and directing it against said screen, means for producing a square wave having the same repetition period as that of the pulses to be received, the rst half cycle of said square wave being identied as the master period. the other half cycle of said square wave being identified as the slave period, index marker producing means for producing a xed index marker that occurs in response to the occurrence of the front edge of the positivev half cycle of said square wave, means for applying said square wave with a certain polarity to said index marker producing means, means for producing a variable index marker pulse that occurs during saidslave period andwhic'h. may be varied to coincidein timelwi-thoneof 'the received pulses, meansv :for producing- Ltwo .slow sweep `defiecting .wavesthat occur .duringsaid square wave half cycles, arespectivelfy, .means ".fo'r .deecting vsaid cathode ray by saidrslow .sweep waves whereby two tracesareproducedon said screen, means for separating .said traees'to .produce an upper and a lower trace, tmeans :for .making ,said fixed marker pulse appear onV one ofbsaid tracesxand for `making said .variable marker. ,pulse Aappear on the other of .said.'traces, K4andmeans .for freversing, at 'thewillof 'theoperator,r said index marker pulses with v.respect .tosaid master.v and slave periods whereby 4saidf iixed index marker pulse occurs vduring saidlslave period `and said variable index 'marker .pulseoccurs during .said master period, :said last .-means'comprising Y switching means ^for reversing the polarity of. -said square wave that vis `applied to said A'fixed :index Ymarker producing means.

'7. In a radio navigation 'receiver for measuring the time interval between 'received pulses, 'a cathode ray .tube indicator -having a Iscreen and having means for Yproducing `a cathode ray and directing it against said screen, land wherein two similar deecting waves, vone of xed timing :and the other of adjustable Atimingfare to Sbe produced for deflecting the cathode ray of said cathode ray tube indicator, 'means rfor producing a Asquare wave having the' same Vrepetition period as the received pulses, the first half cycle of -said square wave 'being lidentified as Athe .master period, lthe other half cycleof said `scruare'wave being identined as the slave period, means ifor'producing a tain an. alignment of' received pulses, and means for Areversing the positions of said index markers with respect to said master and slave periods so that said fixed index marker pulse occurs within said vslave period and said variable index 4marker pulse occurs within said master period, said last means comprising switching means for reversing the polarity of said square wave that is applied to said blanking tube.

8. In a radio navigation receiver for measuring the time interval between received radio pulses, a radio receiver for receiving said pulses,

xed index marker. pulse having a xed phase with respect to saidvmasteriperiod, means for producing .a pulse'xthat is Avariable in time and thatv has a repetition .rate that is twice that of said square wave, ya blanking tube to which Vsaid variable puls'e Vis applied,` said blanking tube having a `pulse :output circuit, means 'for applying saidsquare-wave'witha `certain polarity to acontrol element lof said blanking tube to make it passsignal-during only one half cycle of vsaid square wave `whereby there appears `in said kpulse output circuit said `variable pulse but now 2of the `same repetition `rate as said square wave, means to which 'last 4pulse is applied for producing a variable index marker pulse that may ce adjusted-in `time withinsaid slave'period, means for'producing -saidadjustable deflecting -wave in response to the occurrenceof said variable index marker -pulse whereby the starting time :of said adjustable deflecti-ng wave 'maylbe shifted to oba cathode ray tube indicator vhaving a screen and having means for producing a cathode ray and directing it against said screen, .and wherein two similar defiecting waves, one of fixed timing and the other of adjustable timing, are to be produced for deflecting the cathode ray of said cathode ray tube indicator, means for producing a square wave having the same repetition period as the received pulses, the first half cycle of said square wave .being identied as the master period, the other half cycle of Said square wave being identified as the slavel period, means for producing a fixed index vmarker pulse having a fixed phase :with respect to said master period, means for Aproducing a variable index marker v.pulse that may vbe adjusted in time within said slave period, means for producing said adjustable deflecting wave in response to the occurrence of said variable index marker pulse whereby the start of said adjustable defiecting wave may be shifted to. obtain alignment of the received pulses, switching means for reversing .the positions of said index markers' with respect to said master and slave periods so that said fixed index marker pulse occurs 'within said slave period and said variable index marker pulse occurs within said master period, differential gain vcontrol means for 'said :radio receiver, means for applying 'said square wave to said gain control means whereby theradio ,receiver gain may be increased during said master V'period with .respectto said gain duringsaid slave period Yor Vvice versa, and switching means for reversing the polarity ofthe square wave applied to said gain 'control means. ROBERLTIR. JR.

l REFERENCES rCITED The following references are of record in the ii-le of this patent:

. UNITED STATES 'PATENTS Number v Name Date.

2,487,822 McLamore Nov. A15. 1949 

